qemu: Reformat listen address prior to checking

qemu: Reformat listen address prior to checking

Currently, a listen address for a SPICE server can be specified. Later,
when the domain is migrated, we need to relocate the graphics which
involves telling new destination to the SPICE server. However, we can't
just assume the listen address is the new location, because the listen
address can be ANYCAST (0.0.0.0 for IPv4, :: for IPv6). In which case,
we want to pass the remote hostname. But there are some troubles with
ANYCAST. In both IPv4 and IPv6 it has many ways for specifying such
address. For instance, in IPv4: 0, 0.0, 0.0.0, 0.0.0.0.  The number of
variations gets bigger in IPv6 world. Hence, in order to check for
ANYCAST address sanely, we should take the provided listen address,
parse it and format back in it's full form. Which is exactly what this
patch does.